Microelectromechanical System Oven-controlled Oscillator

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/429,898, filed Dec. 2, 2022, U.S. Provisional Application No. 63/430,615, filed Dec. 6, 2022, U.S. Provisional Application No. 63/434,909, filed Dec. 22, 2022, and U.S. Provisional Application No. 63/434,922, filed Dec. 22, 2022, each of which are incorporated by reference herein for all purposes.

BACKGROUND

An oscillator may be an electronic circuit that produces a periodic signal. An oscillator may be temperature sensitive, because the frequency of oscillation may depend on the physical properties of its oscillating element, which can change with temperature. For example, material properties that control mechanical behavior, such as the stiffness of a spring, the elasticity of a crystal, or the elasticity or dimensions of a microelectromechanical system (MEMS) resonator, are affected by temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

With respect to the discussion to follow and in particular to the drawings, it is stressed that the particulars shown represent examples for purposes of illustrative discussion and are presented in the cause of providing a description of principles and conceptual aspects of the present disclosure. In this regard, no attempt is made to show implementation details beyond what is needed for a fundamental understanding of the present disclosure. The discussion to follow, in conjunction with the drawings, makes apparent to those of skill in the art how embodiments in accordance with the present disclosure may be practiced. Similar or same reference numbers may be used to identify or otherwise refer to similar or same elements in the various drawings and supporting descriptions. In the accompanying drawings:

FIG. 1 illustrates an oven-controlled oscillator, according to some embodiments.

FIG. 2 illustrates another oven-controlled oscillator, according to various embodiments.

FIG. 3 illustrates electronic circuits partitioning, in accordance with some embodiments.

FIGS. 4 - 8 illustrate packages, in accordance with various embodiments.

FIGS. 9 A- 9 D illustrate insulators, according to some embodiments.

FIG. 10 illustrates heaters, according to various embodiments.

DETAILED DESCRIPTION

While this technology is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail several specific embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the technology and is not intended to limit the technology to the embodiments illustrated.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the technology. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

As used herein, “A, B, and/or C” is understood to mean only A, only B, only C, A and B, A and C, B and C, or A, B, and C. In addition, “at least one of A, B, and C” is understood to mean only A, only B, only C, A and B, A and C, B and C, or A, B, and C. In other words, combinations of the elements (e.g., A, B, and C). Additionally or alternatively, “A, B, and/or C” and “at least one of A, B, and C” may mean permutations of the elements (e.g., A, B, and C). There may be any number of elements (e.g., A, B, C, and D; A, B, C, D, and E; etc.).

It will be understood that like or analogous elements and/or components, referred to herein, may be identified throughout the drawings with like reference characters. It will be further understood that several of the figures are merely schematic representations of the present technology. As such, some of the components may have been distorted from their actual scale for pictorial clarity. Moreover, various combinations of the structures, components, materials, and/or elements, other than those specifically shown, are contemplated and are within the scope of the present technology.

Overview

Electronic oscillators are electronic circuits that produce periodic, oscillating electronic signals, such as sine waves and square waves. Electronic oscillators may provide these electronic signals to synchronous digital electronics, such as communications, networking, computing, measurement, and time-keeping circuits and systems. Electronic oscillators may include one or more mechanical resonators (e.g., quartz crystals, microelectromechanical systems (MEMS) resonators, ceramic resonators, and the like), which oscillate with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. For example, a quartz crystal may change its shape under an electric field, which may be referred to as electrostriction or inverse piezoelectricity. By way of further non-limiting example, a MEMS resonator may include a mechanical structure with an inherent resonant frequency that can oscillate by electrostatic or piezoelectric forces to generate a constant frequency.

Electronic oscillators may include circuits that work in conjunction with the resonator to provide periodic, oscillating signals. The resonant frequency of a resonator may vary with temperature. Effects of temperature sensitivity (e.g., changes in frequency over an operating temperature range, such as 0° C. to +70° C., −40° C. to +85° C., −55° C. to +125° C., and the like) may be reduced by keeping the temperature of the resonator within an oven temperature range (e.g., at a target oven temperature, such as 95° C.±1%. Moreover, some circuits (e.g., oscillator circuit, voltage reference, and the like) may benefit from temperature control. Maintaining the resonator and/or circuits at a higher oven temperature range (e.g., 105° C.±1%) may consume more power than at a lower oven temperature range (e.g., 950±1%), because less power from the heaters may be needed to maintain the lower oven temperature range. Additionally or alternatively, heater power may be reduced by limiting the amount of heat lost by the electronic oscillator due to heat leaking out of the oven.

Oven-Controlled Oscillator

FIG. 1 shows oven-controlled oscillator (OCXO) 100 A according to some embodiments. Cavity 120 A may be a temperature-controlled chamber that may maintain resonator(s) 130 A and/or circuit blocks of circuits 140 A within an oven temperature range (e.g., at a target oven temperature, such as 95° C., ±1%), hereinafter referred to as at the target temperature. For example, the target temperature may be selected to be at or higher (e.g., with guard band) than the upper limit of an operating temperature range (e.g., 0° C. to +70° C., −40° C. to +85° C., −55° C. to +125° C., and the like). The operating temperature range may be a range of temperatures outside of package 110 A at which OCXO 100 A may function within predetermined specifications, such as in a datasheet. Heater(s) 144 A (and/or a heater(s) in resonator(s) 130 A (not depicted in FIG. 1 )) may generate heat to raise and/or maintain resonator(s) 130 A and/or circuit blocks of circuits 140 A at the target temperature. In this way, a temperature experienced by resonator(s) 130 A and/or circuit blocks of circuits 140 A may be consistently higher than a temperature outside of package 110 A. The temperature outside of package 110 A may be referred to as the ambient temperature. Effects of changes to the ambient temperature on resonator(s) 130 A and/or circuit blocks of circuits 140 A may be limited by OCXO 100 A.

As shown, resonator 130 A may be coupled to electronic circuits 140 A and electronic circuits 140 A may be coupled to insulator (separator) 150 A, such as by using die attach. Die attach may be an adhesive die attach (e.g., polyimide, epoxy, silicone, and the like, and may contain fillers to optimize combinations and permutations of thermal, mechanical, and electrical properties of the adhesive), eutectic die attach (e.g., eutectic alloy), or other type of die-to-die bonding. Heat may be lost from resonator(s) 130 A through bond wires 122 A, from electronic circuits 140 A through bond wires 124 A and insulator 150 A, and from cavityl 20 A through package 110 A (including lid 112 A). Package 110 A may thermally insulate (e.g., have a thermal resistance θ>100° C./W) resonator 130 A and/or circuit blocks of circuits 140 A from the environment outside of package 110 (e.g., ambient temperature).

By way of non-limiting example, resonator(s) 130 A and/or circuits 140 A may be semiconductor die (e.g., a small piece of semiconducting material on which a resonator(s) and/or circuits may be fabricated, such as silicon, carbon (e.g., diamond, diamond-like carbon, carbon nanotubes, and graphite), silicon germanium, germanium, III-V compounds (e.g., composed boron, aluminum, gallium, indium, nitrogen, phosphorous, arsenic, and tin), and the like). Additionally, other compound semiconductors from columns 4 , 13 , 14 , and 15 of the periodic table of the elements, such as silicon carbide, aluminum nitride, and (oxides of) zirconium and halfnium, may be used. Moreover, various doping levels may be applied to the foregoing materials. Resonator(s) 130 A may optionally include temperature sensor(s) 132 A. Circuits 140 A may optionally include temperature sensor(s) 142 A. Bond wires 122 A and bond wires 124 A may provide interconnections between resonator 130 A and circuits 140 A, and circuits 140 A and package 110 A, respectively. Bond wires 122 A and bond wires 124 A may each comprise combinations and permutations of aluminum, copper, silver, gold, and the like. Other interconnections, such as solder balls, through-silicon vias (TSVs), and the like may be used. Package 110 A may be a ceramic package (e.g., Alumina (Al2O3) multilayered ceramic package), a plastic package (e.g., small outline integrated circuit (SOIC), small outline transistor (SOT), quad flat no-lead (QFN), and the like package), and/or a metal package (e.g., TO- 3 , TO- 41 , and the like). Lid 112 A may be plastic, metal, combinations thereof, or other materials.

Electronic circuits 140 A may operate in conjunction with resonator(s) 130 A to produce periodic, oscillating electronic signals. For example, electronic circuits 140 A may include sustaining amplifiers having a gain. The sustaining amplifiers may drive resonator 130 A in continuous motion and produce output signals at approximately the resonant frequency for the synchronous digital electronics (not depicted in FIG. 1 ). Electronic circuits may additionally perform temperature compensation, frequency synthesis, temperature measurement, heater control, clock distribution, and the like. By way of non-limiting example, electronic circuits 140 A may include combinations and permutations of buffers, heaters, amplifiers, volatile and non-volatile memories, filters, phase-locked loops (PLLs), voltage-controlled oscillators (VCOs), analog to digital converters (ADCs), digital to analog converters (DACs), and the like.

Electronic circuits 140 A may generate heat (in addition to heat generated by heater(s) 144 A). For example, circuits 140 A may consume on the order of 10-200 mW which may heat cavity 120 A by 1°−20° C. In this way, the electronic oscillator may be said to be self-heating. Accordingly, the target temperature may additionally or alternatively be selected to be the maximum of the operating temperature range plus an amount of heat produced by self-heating plus guard band.

The amount of heat produced by heater(s) 144 A may be reduced by limiting the amount of self-heating, because the target temperature may be set lower (than with more self-heating). In this way, power consumed by heater(s) 144 A may be reduced, and OCXO 100 A may consume less power. As described below, the amount of power consumed by circuits 140 A may be advantageously reduced by moving some circuit blocks to another circuits die that is not temperature controlled. For example, within the same OCXO there may be a “heated” portion which is temperature controlled and a “non-heated” portion which is not temperature controlled. The circuits die in the “heated” portion may have fewer circuit blocks and hence consume less power than, for example, circuits 140 A. Self-heating in the circuits die in the “heated” portion may also be accordingly reduced. The target temperature may be lowered because the self-heating is lowered.

In addition, when the power consumption of the circuits die is large, it may limit the maximum thermal resistance of, for example, package 110 A and/or insulator 150 A, as the self-heating may increase with increased thermal resistance. When the heat produced by circuits 140 A plus the ambient temperature is higher than the target temperature, resonator(s) 130 A and/or circuit blocks of circuits 140 A may not operate at the target temperature. Recall that OCXOs are supposed to keep the resonator and/or some circuit blocks operating at the target temperature. Accordingly, the thermal resistance of insulator 150 A and/or package 110 A may be reduced to lower the temperature of resonator(s) 130 A and/or circuit blocks of circuits 140 A down to the target temperature. When OCXO 100 A starts up at the ambient temperature, heater(s) 144 A may consume more power to heat resonator(s) 130 A and/or circuit blocks of circuits 140 A to the target temperature, because heat generated by heater(s) 144 A may leak out through insulator 150 A and/or package 110 A due to their lower thermal resistance.

However, when the power consumption of the “heated” circuits is reduced, the thermal resistance of package 110 A and insulator 150 A may be increased. This may also lead to lower overall power consumption of OCXO 100 A because heater(s) 144 A may consume less power. Less power may be needed from heater(s) 144 A to heat resonator(s) 130 A and/or circuit blocks of circuits 140 A to the target temperature, because less heat leaks through insulator 150 A and/or package 110 A due to their higher thermal resistance.

Heated and Non-Heated Partitioning

FIG. 2 shows OCXO 100 B according to some embodiments. OCXO 100 B, except as noted below, may have at least some of the characteristics of OCXO 100 A ( FIG. 1 ). OCXO 100 B may include heated section 210 B and non-heated section 220 B. Here, heated may refer to heating using heaters (e.g., heater(s) 144 B) and non-heated may refer to not heating with heaters (although there may be self-heating). Heated section 210 B may include package 110 B. Package 110 B may include lid 112 B. Heated section 210 B may be heated to the target temperature by combinations and permutations of heater(s) 144 B, a heater(s) in resonator(s) 130 B 1 (not shown in FIG. 2 ), and self-heating. Connections 114 B and 232 B may each be combinations and permutations of pins, solder balls, and the like, and may provide interconnections between package 110 B and substrate 240 B, and package 230 B and substrate 240 B, respectively. Substrate 240 B may provide interconnections between package 110 B and package 230 B. Resonator(s) 130 B 1 may optionally include one or more temperature sensors 132 B. Circuits 140 B 1 may optionally include one or more temperature sensors 142 B. Non-heated section 220 B may include package 230 B. Package 230 B may be a ceramic package (e.g., Alumina (Al2O3) multilayered ceramic package), a plastic package (e.g., SOIC, SOT, QFN and the like package), and/or a metal package (e.g., TO- 3 , TO- 41 , and the like).

Substrate 240 B may be a medium having one or more layers, such as a printed circuit board, which may connect electronic components-such as package 110 B, package 230 B, and optionally other electronic components (not shown in FIG. 2 )—to one another. For example, substrate 240 B may be comprised of combinations and permutations of aluminum, copper, ceramic, phenolic paper (e.g., FR- 1 and FR- 2 ), woven fiberglass (e.g., FR- 4 ), polyimide foil, polyimide-fluoropolymer composite foil, and the like. Cover 250 B may enclose package 110 B and/or package 230 B on substrate 240 B, for example, to provide physical protection from environmental conditions such as moisture, impacts, and the like. Cover 250 B may be plastic, metal, combinations thereof, or other materials. By way of further non-limiting example, cover 250 B may be optional or encapsulation. Thermal vias 242 B may be small holes through substrate 240 B filled with a thermally conductive material, such as copper and/or aluminum. Thermal vias 242 B may act as a heatsink and draw heat from package 230 B.

As shown, there may be circuits 140 B 1 in heated section 210 B and circuits 140 B 2 in non-heated section 220 B. Constituents of circuits 140 A ( FIG. 1 ) may be divided between circuits 140 B 1 and circuits 140 B 2 . For example, operation of resonator 130 B 1 may benefit from having constituents of circuits 140 A close to resonator 130 B 1 (e.g., in heated section 210 B). Other constituents of circuits 140 A-which may not benefit operation of resonator 130 B 1 by being disposed in heated section 210 B and/or may contribute to self-heating—may be disposed in non-heated section 220 B. For example, constituents of circuits 140 B 1 may consume on the order of 1-10 mW, not including heater 144 B, whereas constituents of circuits 140 B 2 may consume on the order of 10-200 mW.

Optional resonator(s) 130 B 2 may be coupled to circuits 140 B 2 . Although heater 144 B is shown in circuits 140 B 1 , alternatively or additionally there may be a heater in resonator(s) 130 B 1 (not shown in FIG. 2 ).

Cavity 120 B may be filled with a fluid having a lower thermal conductivity than, for example, air (26.2 mW/(m K)) and/or nitrogen gas (26.0 mW/(m K)). In this way, heat loss through cavity 120 B may be decreased and heater power consumption may be reduced. Gases having a relatively low thermal conductivity, such as (combinations and permutations of) xenon (Xe; 5.5 mW/(m K), P=0), krypton (Kr; 9.5 mW/(m K), P=0), dichlorodifluoromethane (CCl 2 F 2 ; 9.9 mW/(m K)), carbon dioxide (CO 2 ; 16.8 mW/(m K)), and argon (Ar; 17.9 mW/(m K)), may be used to fill cavity 120 B. Except where noted, the example thermal conductivities of gases are at 300° K and pressure P=1 bar. By way of further non-limiting example, a vacuum (e.g., 1.0 Ba>P>1.0 μBa) may be in cavity 120 B (e.g., package 110 B may be vacuum sealed). It will be apparent to one of ordinary skill in the art that large-molecule and/or large-atomic gasses (and combinations and permutations thereof) often may have low thermal conductivity. Accordingly, the foregoing list is provided by of example and not limitation.

Combinations and permutations of low thermal conductivity gasses and vacuum may be used together in cavity 120 B. This may provide a lower thermal conductivity than one gas and/or vacuum alone. Optimal gas selection criteria may include: not chemically reactive (not reactive with package 110 B and/or contents of package 110 B), chemically inert, environmentally friendly, non-toxic, manageable in a package assembly environment, low cost, and the like.

An additional benefit of large-molecule and/or large-atomic gasses is that they may be more readily sealed and have lower leak rates than small-molecule and/or small-atomic gasses, such as H 2 (small molecule) and/or He (small atomic). Accordingly, using the large-molecule and/or large-atomic gasses may result in improved package durability and reliability.

Package 110 B may be sealed to keep the gas and/or vacuum in cavity 120 B. For example, package 230 B may be hermetically sealed.

Resonator(s) 130 B 1 may be other MEMS devices that may benefit from thermal management. By way of illustration and not limitation, resonator(s) 130 B 1 may be a gyroscope, accelerometer, vibrometer, magnetic field sensor, transducer, chemical detector, and/or other MEMS devices. A chemical detector may be a gas sensor (e.g., hydrogen, helium, ammonia, carbon monoxide, carbon dioxide, nitrogen oxides, and various pollutants). OCXO 100 B may expose the MEMS devices (e.g., resonator(s) 130 B 1 ) to the gas (e.g., lid 112 B and/or cover 250 B may be permeable to the gas and/or vented).

Circuits Partitioning

FIG. 3 shows OCXO 100 C according to some embodiments. FIG. 3 illustrates a partitioning of electronic circuits functions/operations among circuits 140 C 1 (e.g., in heated section 210 B ( FIG. 2 )) and circuits 140 C 2 (e.g., in non-heated section 220 B ( FIG. 2 )), according to some embodiments. OCXO 100 C may have at least some of the characteristics of OCXO 100 A and 100 B ( FIGS. 1 and 2 ).

As shown, circuits 140 C 1 in package 110 C may be connected to resonator(s) 130 C 1 . Resonator(s) 130 C 1 may optionally include one or more temperature sensors 132 C and/or one or more heaters 134 C. A periodic, oscillating signal(s) generated using resonator(s) 130 C 1 may be provided by circuits 140 C 1 to circuits 140 C 2 through CLK signal 350 , referred to hereinafter as a reference clock. Circuits 140 C 1 and circuits 140 C 2 may communicate (e.g., sensor, status/state, and control information) with each other through communications 330 . For example, communications 330 may be combinations and permutations of discrete signals (e.g., temperature sensor 142 C and/or 132 C output from circuits 140 C 1 to circuits 140 C 2 , heater control from circuits 140 C 2 to circuits 140 C 1 , data from system logic 328 (e.g., RAM and/or ROM), and the like), serial busses (e.g., Serial Peripheral Interface (SPI), I2C, and the like), parallel busses, and the like.

Circuits 140 C 1 may include sustaining circuit(s) 310 , optional temperature sensor 142 C, heater driver 312 , and heater(s) 144 C. Sustaining circuit(s) 310 may initiate and maintain periodic oscillations in resonator(s) 130 C 1 . For example, sustaining circuit(s) 310 may be one or more amplifiers having a gain greater than 1. Optional temperature sensor 142 C may sense a temperature in circuits 140 C 1 which may be used to determine a temperature of resonator(s) 130 C 1 and/or circuit blocks of circuits 140 C 1 . Optional temperature sensor 142 C may be combinations and permutations of a resistive-based temperature sensor (e.g., Resistance Temperature Detector (RTD) or similar), a discrete circuit-based sensor (e.g., bipolar junction transistor (BJT), diode (bipolar junction), MOSFET transistor, or similar), and other type of temperature sensors (e.g., thermocouple, thermopile, acoustic velocity thermometer, variable conductance thermometer, variable capacitance thermometer, variable inductance thermometer, and the like). Optional temperature sensor 132 C may sense a temperature on a silicon die of resonators 130 C 1 . Optional temperature sensor 132 C may be combinations and permutations of a resonator whose resonant frequency varies with temperature in a predetermined manner, a resistive-based temperature sensor (e.g., Resistance Temperature Detector (RTD) or similar), a discrete circuit-based sensor (e.g. BJT or similar), and other type of temperature sensor.

For example, resonator(s) 130 C 1 may be a temperature stable resonator (e.g., variation on the order of 1 PPM/° C. or less) and temperature sensor 132 C may be a temperature sensitive resonator (e.g., variation on the order of 5 PPM/° C. or less). In some embodiments, the temperature stable resonator and the temperature sensitive resonator may be in one resonator having temperature stable and temperature sensitive resonant modes. The periodic signals from the temperature stable and temperature sensitive resonators/modes may be processed to produce a temperature compensated reference periodic signal and temperature measurement. The examples for temperature stability (e.g., 1 PPM/° C.) and temperature sensitivity (e.g., 5 PPM/° C.) are provided for illustrative purposes. Other examples, where the temperature stability and temperature sensitivity are different values may be used. A temperature sensor using MEMS resonators is described further in U.S. Pat. No. 10,247,621 titled “High Resolution Temperature Sensor” which is incorporated by reference herein for disclosure of temperature sensing.

Heater driver 312 may control the amount of heat generated by heater(s) 144 C and/or heater(s) 134 C. For example, heater driver 312 may be an electronic current control circuit that supplies varying electronic current based on the temperature as measured by temperature sensor 132 C and/or 142 C. Heater(s) 144 C and/or heaters 134 C may produce heat to maintain resonator(s) 130 C 1 and/or circuit blocks of circuits 140 C 1 at the target temperature. For example, heater(s) 144 C and/or heaters 134 C may be combinations and permutations of diffused resistors, ion-implanted resistors, thin-film resistors, polysilicon resistors, transistors (e.g., BJT and MOSFET), and the like. By way of non-limiting example, circuits 140 C 1 may consume on the order of 1-10 mW and raise the temperature in package 110 C on the order of 1-10° C. (e.g., due to self-heating), not including the effects of heaters 144 C and heaters 134 C.

Circuits 140 C 2 may include optional sustaining circuit(s) 320 , digitally controlled oscillator 321 , temperature compensation 322 , heater control 324 , output driver(s) 326 , and system logic 328 (e.g., volatile memory (e.g., RAM, DRAM, SRAM, and the like), non-volatile memory (e.g., ROM, EEPROM, FLASH, and the like), processor (e.g., logic, state machine, microprocessor, and the like), communications port (e.g., SPI, I2C, and the like), etc.). The communications port in system logic 328 may communicate with an external computer system before and/or after the electronic oscillator is sold to configure circuits 140 C 2 . For example, coefficients used by temperature compensation 322 may be programmed into a memory of system logic through communications 340 and communications port in system logic 328 . By way of further non-limiting example, an end user may configure an output frequency through communications 340 and communications port in system logic 328 .

Optional sustaining circuits 320 may initiate and maintain periodic oscillations in optional resonator(s) 130 C 2 . For example, optional sustaining circuit(s) 320 may be one or more amplifiers having a gain greater than 1. Digitally controlled oscillator 321 may use the reference clock generated by circuits 140 C 1 as an input and may perform functions such as reducing the jitter from clock generated by circuits 140 C 1 , providing synthesis of other clock frequencies based on the clock generated by circuits 140 C 1 , enable the ability to adjust the clock frequency based on the input through communications port 340 , and the like. For example, digitally controlled oscillator 321 may include a voltage-controlled oscillator (VCO) driven by a control signal from a digital-to-analog converter (not depicted in FIG. 3 ). Optional resonator(s) 130 C 2 may communicate with circuits 140 C 2 . For example, optional resonator(s) 130 C 2 may provide a low-jitter clock reference to digitally controlled oscillator 321 .

Temperature compensation 322 may compensate for changes in the resonant frequency of resonator(s) 130 C 1 over its operating temperature range. In operation, heater(s) 144 C may produce heat to maintain resonator(s) 130 C 1 and/or circuit blocks of circuits 140 C 1 at the target temperature. When OCXO 100 C starts up (e.g., OCXO 100 C is at ambient temperature and not at the target temperature) or when the ambient temperature changes/fluctuates, the temperature of resonator(s) 130 C 1 and/or circuit blocks of circuits 140 C 1 may not be at the target temperature. Here, for example, the relationship between temperature and frequency of the resonator(s) 130 C 1 may be approximated by a polynomial function. The polynomial function may approximate the change from the desired frequency at a particular temperature (e.g., determined by temperature sensor 132 C and/or temperature sensor 142 C) and the digitally controlled oscillator 321 may adjust its frequency multiplication value based on the output of the polynomial function to compensate for the change in frequency produced by resonator(s) 130 C 1 due to the deviation from the target temperature.

Heater control 324 may determine the temperature of resonator(s) 130 C 1 and/or circuit blocks of circuits 140 C 1 using output from temperature sensor 132 C and/or temperature sensor 142 C and control (e.g., increase, decrease, and/or maintain an amount of heat generated by) heater(s) 144 C and/or heaters 134 C. Heater control may generate an analog and/or digital control signal (e.g., a digital value that corresponds to the amount of heater current) and provide it to heater driver 312 through communications 330 .

Output driver(s) 326 may produce an output signal for the electronic oscillator. The output signal may be generated using combinations and permutations of resonator(s) 130 C 1 , resonator(s) 130 C, temperature compensation 322 , and digitally controlled oscillator 321 . Output driver(s) 326 may include combinations and permutations of a current-controlled switch, voltage-controlled switch, bipolar junction transistor (BJT), junction-gate field-effect transistor (JFET), (n- and/or p-type) metal-oxide-semiconductor field-effect transistor (MOSFET), and the like. By way of non-limiting example, output driver(s) 326 may be a complementary metal-oxide-semiconductor (CMOS) inverter, totem pole output, and the like to produce combinations and permutations of CMOS, TTL, LVCMOS, and the like signals at output 360 . By way of further non-limiting example, output driver(s) may additionally or alternatively be differential, such as combinations and permutations of low-voltage differential signaling (LVDS), low-voltage positive emitter-coupled logic (LVPECL), current mode logic (CML), and the like at output 360 .

While solder bumps for interconnect-between resonator(s) 130 C 1 and circuits 140 C 1 , and resonator(s) 130 C 2 and circuits 140 C 2 —are depicted in FIG. 3 , other interconnect may be used, such as bond wires.

Although circuits 140 C 1 and circuits 140 C 2 are depicted as having certain functions (e.g., sustaining circuit(s) 310 , optional temperature sensor 142 C, heater driver 312 , heater(s) 144 C, optional sustaining circuit(s) 320 , digitally controlled oscillator 321 , temperature compensation 322 , heater control 324 , output driver(s) 326 , system logic 328 ), it is understood that combinations and permutations of the functions may be partitioned among circuits 140 C 1 and circuits 140 C 2 . By way of non-limiting example, heater control 324 may be in circuits 140 C 1 .

Package

As illustrated in FIG. 2 , package 110 B of heated section 210 and package 230 B of non-heated section 220 B may be disposed planarly (e.g., adjacent to each other, side by side, and the like) on substrate 240 B. Heated section 210 and non-heated section 220 B may have other spatial orientations. By way of non-limiting example, heated section 210 and non-heated section 220 B may be oriented vertically. FIGS. 4 - 8 illustrate OCXOs 100 D- 100 H having vertically oriented heated and non-heated sections, according to some embodiments. Each of OCXOs 100 D- 100 H may have at least some of the characteristics of OCXOs 100 A- 100 C ( FIGS. 1 - 3 ), vice-versa, and each other.

FIG. 4 shows OCXO 100 D including package 110 D oriented above substrate 240 D. Package 110 D may be in a heated section (e.g., heated section 210 in FIG. 2 ) and include lid 112 D, connections 114 D, cavity 120 D, resonators 130 D 1 , circuits 140 D 1 , and insulator (separator) 150 D. Substrate 240 D may be in a non-heated section (e.g., non-heated section 220 B in FIG. 2 ) and include resonator(s) 130 D 2 and circuits 140 D 2 .

Circuits 140 D 1 may be electrically and/or thermally coupled to package 110 D through bond wires 122 D. Package 110 D may be electrically and/or thermally coupled to substrate 240 D through connections 114 D. Substrate 240 D may be electrically and/or thermally coupled to another substrate, package, module, and the like, such as through pins, solder balls, and the like (not depicted in FIG. 4 ).

Package 110 D may include cavity 120 D′ beneath insulator 150 D. Since insulator 150 D may not make physical contact with package 110 D where insulator 150 D is above cavity 120 D′, the amount of heat leaking out of package 110 D through insulator 150 D may be reduced.

As shown, substrate 240 D may include a cavity/indentation so that there is sufficient clearance for package 110 D to be disposed above resonator(s) 130 D 2 and/or circuits 140 D 2 . Thermal vias in substrate 140 D (not depicted in FIG. 4 ) may act as a heatsink for heat produced by resonator(s) 130 D 2 and/or circuits 140 D 2 .

Bond wires 122 D, connections 232 D 1 , connections 232 D 2 , and connections 410 D may be combinations and permutations of bond wires, solder balls, through-silicon vias (TSVs), and the like. For example, bond wires 510 may electrically and/or thermally couple circuits 140 E 2 to substrate 240 E, as shown in FIG. 5 . As shown, substrate 240 E may include a cavity/indentation so that there is sufficient clearance for package 110 E to be disposed above bond wires 510 , resonator(s) 130 E 2 , and/or circuits 140 E 2 . Package 110 F in FIG. 6 may include a cavity to provide space for resonator(s) 130 F 2 and/or circuits 140 F 2 . Solder balls may electrically couple resonator(s) 130 F 2 and/or circuits 140 F 2 to substrate 240 F. Bond wires, through-silicon vias (TSVs), and the like may alternatively or additionally be used. For example, bond wires 610 may electrically and/or thermally couple circuits 140 G 2 to substrate 240 G, as shown in FIG. 7 .

FIG. 8 shows OCXO 100 H according to some embodiments. As shown, resonator(s) 130 H 2 and/or circuits 140 H 2 may be disposed (e.g., mounted/attached) on a surface of substrate 240 H that is opposite of a surface of substrate 240 H upon which package 110 H is disposed (e.g., mounted/attached). Connections 810 may have sufficient size to create a space for resonator(s) 130 H 2 and/or circuits 140 H 2 (e.g., so there is room for them when OCXO 100 H is mounted to another substrate, module, package, and the like). Connections 810 may be combinations and permutations of solder balls, pins, and the like.

Insulator

Referring back to FIG. 2 , package 110 B may advantageously have a high thermal resistance, for example, so that less power is consumed to maintain the target temperature. In contrast, package 230 B may advantageously have a low thermal resistance, for example, to dissipate the heat produced by circuits 140 B 2 . Substrate 240 B may be designed to advantageously minimize thermal crosstalk between package 110 B and package 230 B. For example, substrate 240 B may be relatively thermally insulative around package 110 B and substrate 240 B may be relatively thermally conductive about package 230 B. By way of further non-limiting example, the metal layer(s), metal trace(s), and/or via(s) (e.g., density, quantity, dimensions, geometry, placement, and the like) may be designed for optimal thermal characteristics.

In general, ceramic packages may have a thermal resistance-between the semiconductor die inside the package to the circuit board on which the package is mounted (from junction to ambient), referred to as θ JA -on the order of 30° C./W to 100° C./W. Typically, most (e.g., >95%) of heat may dissipate from the semiconductor die to the bottom of the ceramic package to the connections (e.g., solder balls, pins, and the like) to the circuit board. Generally, heat dissipation from bond wires may be negligible (e.g., <5%).

In contrast, package 110 B may advantageously have a θ JA on the order of 100° C./W to 1500° C./W. In package 110 B, heat may dissipate through the bottom of package 110 B (e.g., ˜20%-80%), through bond wires 124 B (˜10%-50%), and gas/vacuum in cavity 120 B (˜10%-50%). The thermal resistance through the bottom of package 110 B may be increased by having one or more of insulator 150 B. Additionally or alternatively, bond wires 124 B may be thinner to increase the thermal resistance in this path.

FIGS. 9 A- 9 D show insulator examples 900 A- 900 D (respectively) from top/bottom and side views, according to some embodiments. Insulator examples 900 A- 900 D may include circuits 910 A- 910 D and insulators 920 A- 920 D. Circuits 910 A- 910 D may have least some of the characteristics of circuits 140 B 1 in FIG. 2 and/or circuits 140 C 1 in FIG. 3 , and vice versa. Insulators 920 A- 920 D may have at least some of the characteristics of insulator 150 B in FIG. 2 , and vice versa. Insulators 920 A- 920 D may each comprise low thermal expansion glasses, low thermal expansion ceramics, and the like. By way of non-limiting example, insulators 920 A- 920 D may comprise a material having a thermal resistance less than 2 W/(m K), where W is Watts, m is meters, and K is a temperature in Kelvin.

FIG. 9 A depicts small size insulator 920 A. FIG. 9 B illustrates large/equal size insulator 920 B. The sizes may be relative to circuits 910 A and 910 B, which may be semiconductor die. Small size insulator 920 A may advantageously have a thermal resistance on the order of 100° C./W to 1500° C./W. Alternatively or additionally, small size insulator 920 A may advantageously isolate circuits 140 B 1 from stress from package 110 B. In contrast, large/equal size insulator 920 B may have a thermal resistance on the order of 100° C./W to 300° C./W.

FIG. 9 C shows insulators 920 C and 930 C stacked. FIG. 9 D depicts parallel insulators 920 D. Stacked insulators 920 C and 930 C together may advantageously have a thermal resistance on the order of 200° C./W to 1500° C./W. Although two insulators are provided as an example, more insulators may be stacked. Parallel insulators 920 D may advantageously have a thermal resistance on the order of 200° C./W to 1000° C./W. It will be understood that combinations and permutations of multiple insulators having different sizes, being stacked, and/or being in parallel may be used.

Heater

FIG. 10 shows heater example 1000 , according to some embodiments. Heater example 100 is provided by way of example and not limitation. Heater example 1000 may include circuits 1010 , resonator(s) 1020 , and bond pads 1040 . Circuits 1010 may include heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 . Circuits 1010 may have at least some of the characteristics of circuits 140 B 1 in FIG. 2 , circuits 140 C 1 in FIG. 3 , and/or circuits 910 A- 910 D in FIGS. 9 A- 9 D , and vice versa. Resonator(s) 1020 may have at least some of the characteristics of resonator(s) 130 A in FIG. 1 , resonator(s) 130 B 1 in FIG. 2 , and/or resonator(s) 130 C 1 in FIG. 3 , and vice versa. Heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 may have at least some of the characteristics of heater 144 A in FIG. 1 , heater 144 B in FIG. 2 , and/or heater 144 C in FIG. 3 , and vice versa.

One or more of heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 may be used to provide heat to resonator(s) 1020 . For example, there may be one of or combinations of heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 . Although heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 are shown having a length of an adjacent side of resonator(s) 1020 , they may each be longer or shorter. Heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 may each be combinations and permutations of diffused resistors, ion-implanted resistors, thin-film resistors, polysilicon resistors, and the like. Heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 may be segmented, for example, divided into sections which may be individually or collectively controlled (not shown in FIG. 10 )

Heat from circuits 1010 may be conducted through package bond pads 1040 XX and bond wires (not shown in FIG. 10 ). To prevent thermal gradients (e.g., temperatures differences across regions of circuits 1010 and resonator(s) 1020 ) from forming the disposition of bond pads 1040 on circuits 1010 may be symmetric. For example, when circuits 1010 is viewed in halves, there may be an equal number of bond pads 1040 on both halves. By way of further non-limiting example, the foregoing symmetric quantity and placement may yield a thermal gradient across circuits 1010 and/or resonator(s) 1020 on the order of 10.0 E-3° C. or less which may be referred to as a uniform thermal gradient.

Although bond pads 1040 are shown being of equal size and equal distance from each other, bond pads 1040 may be of different sizes, quantities, and spacing from each other. Bond wires associated with bond pads 1040 may also have different lengths. The size, number, and spacing of bond pads 1040 and the bond wires associated with bond pads 1040 may be designed for uniform thermal conductivity and hence uniform temperature across circuits 1010 and resonator(s) 1020 . The size, number, and placement of heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 may be adjusted to compensate for asymmetric thermal conduction through bond pads 1040 and bond wires associated with bond pads 1040 . In operation, the power provided to each of heaters 1030 A- 1 , 1030 A- 2 , 1030 B- 1 , and/or 1030 B- 2 may be controlled to compensate for asymmetric thermal conduction through bond pads 1040 and bond wires associated with bond pads 1040 . The foregoing techniques may, for example, yield a thermal gradient across circuits 1010 and/or resonator(s) 1020 on the order of 1.0 E-3° C. or less which may be referred to as a highly uniform thermal gradient.